Host-to-host
A direct file link between a company's ERP and its bank, moving payment orders and statements automatically without anyone logging into online banking.
In practice it is almost always SFTP. The company drops payment files into a directory on the bank's server, the bank drops status reports and statements back, and the files are encrypted and signed with PGP on top. AS2 turns up occasionally instead. The formats these days are mostly ISO 20022 messages such as pain.001 and camt.053, although bank-specific dialects and legacy formats linger longer than anyone would like.
The upside is that there is no membership fee and the bank usually helps set it up. The downside is that every bank is its own integration project, with its own keys, its own folder names and its own reading of the standard. A group with twelve banks therefore has twelve host-to-host links, which is exactly the problem EBICS in Germany and Swift for corporates set out to solve.